At present, people living in cities of industrialized countries have enjoyed a variety of life styles and have acted in various time cycles. Accompanied with increasing population, housings have been concentrated in cities in particular; hence, there is a tendency that noise pollution increases not only with respect to inmate family members but with respect to surrounding people. For example, when a viewer watches and listens to an audio-visual device (e.g., a television receiver) so as to generate a relatively large volume of sound in the night, noise pollution occurs which can cause annoyance for other persons other than the viewer. In terms of the protection of privacy of people, it is necessary to reduce the noise pollution.
Until now, a viewer may pay attention to avoid causing noise pollution to the neighboring persons by reducing sound volume; however, when sound volume is simply reduced, there is a disadvantage in that it may be difficult to hear the audio contents (or programs).
When a viewer is at a place distanced from an audio-visual device (e.g., a kitchen distanced from a living room), or when an aged person having poor hearing watches and listens to an audio-visual device, it is necessary to adequately increase the sound volume. However, when a viewer at a surrounding position of the audio-visual device or a viewer having adequate hearing watches and listens to the same contents (or programs) together with the others, there is a problem in that discomfort may occur by the increasing sound volume. In addition, increasing the sound volume may cause noise pollution with respect to inmate family members having no intention to watch and listen to the contents (or programs) and with respect to neighboring persons.
In order to solve the aforementioned problems, local speaker amplifiers arranged in the surrounding areas of specific viewers are put to practical use (see Non-patent document 1). Non-patent document 1: “Mimimoto-kun α mild in ears”, which can be retrieved online via the Internet: URL: http://home.s00.itscom.net/large/CS-30P/.
However, the device disclosed in the Non-patent document 1 is constituted using an amplifier speaker (or an earphone) arranged in the surrounding area of a specific viewer; hence, it is necessary to connect the device with a television receiver via a cable. Thus, the cable and amplifier speaker may cause disturbance and are troublesome to set up.